Glucose exerts opposite effects on mRNA versus protein and activity levels of Pde1, the low-affinity cAMP phosphodiesterase from budding yeast, Saccharomyces cerevisiae

AbstractIn budding yeast (Saccharomyces cerevisiae), a low-affinity phosphodiesterase, Pde1, and a high-affinity phosphodiesterase, Pde2, are responsible for the degradation of cAMP. Addition of glucose to glycerol-grown yeast cells is known to cause a transient increase in the cAMP level and recent work has indicated a specific involvement of Pde1 in this response. In this work we show that glucose addition induces the accumulation to high levels of mRNA encoding Pde1. This increase continues for at least 8 hours and is due to enhanced transcription of the PDE1 gene, since glucose addition does not change the stability of the Pde1 mRNA. Surprisingly, using an assay method specific for Pde1, we observed that the activity of Pde1 remains constant and finally decreases several-fold during the same period. In addition, this activity profile closely follows the Pde1 protein level as judged from Western blotting with antibodies directed against Pde1. Experiments using cycloheximide, a general inhibitor of translation, allow to exclude the possibility of a futile cycle of Pde1 synthesis and degradation. Hence, glucose addition appears to trigger an increase in PDE1 gene transcription together with a specific inhibition of the translation of Pde1 mRNA